IOError with lxml etree parse function

I have a logic like ：

for root, dirs, files in os.walk(os.getcwd()):
    if "info.xml" in files:
        root = lxml.etree.parse("%s/info.xml" % root)
        tag = root.xpath("/info/tagname")[0].text

when parse one info.xml which very deep in current path, met Error Message:

    Traceback (most recent call last):
  File "/home/work/merge开发者_JAVA技巧file.py", line 365, in <module>
  File "/home/work/mergefile.py", line 344, in merge_ejb_files
  File "/home/work/mergefile.py", line 63, in __init__
  File "/home/work/mergefile.py", line 78, in _parse_info2doc
  File "lxml.etree.pyx", line 2698, in lxml.etree.parse (src/lxml/lxml.etree.c:49590)
  File "parser.pxi", line 1491, in lxml.etree._parseDocument (src/lxml/lxml.etree.c:71205)
  File "parser.pxi", line 1520, in lxml.etree._parseDocumentFromURL (src/lxml/lxml.etree.c:71488)
  File "parser.pxi", line 1420, in lxml.etree._parseDocFromFile (src/lxml/lxml.etree.c:70583)
  File "parser.pxi", line 975, in lxml.etree._BaseParser._parseDocFromFile (src/lxml/lxml.etree.c:67736)
  File "parser.pxi", line 539, in lxml.etree._ParserContext._handleParseResultDoc (src/lxml/lxml.etree.c:63820)
  File "parser.pxi", line 625, in lxml.etree._handleParseResult (src/lxml/lxml.etree.c:64741)
  File "parser.pxi", line 563, in lxml.etree._raiseParseError (src/lxml/lxml.etree.c:64056)
IOError: Error reading file '/home/work/ci/case/dc_daily/dc/213577/223922/223958/792536/info.xml': failed to load external entity "/home/work/ci/case/dc_daily/dc/213577/223922/223958/792536/info.xml"

but the file "/home/work/ci/case/dc_daily/dc/213577/223922/223958/792536/info.xml" exist and I can parse it with lxml under ipython IDE

Do you know what is the problem is? If you know it, help me please! Thank you!

---

Here's my solution, as per my comment above. I'm opening files for read, them closing them right after so I don't hit the 1024 file limit.

import lxml.etree as etree
for root,dirs,files in os.walk(os.getcwd()):
    if "info.xml" in files:
        with open('%s/info.xml'%root) as processfile: #use 'rb' if necessary
            xml = etree.parse(processfile)
            tag = root.xpath("/info/tagname")[0].text